The major goal of this proposal is the understanding of the nature of higher order color mechanisms. By higher order mechanisms are meant elements in the chain of visual lprocessing beyond the second stage mechanisms of most conventional models of vision. The existence of such mechanisms has been suggested by the detailed analysis of the selective desensitization resulting from the viewing of modulated fields, and by the relation between the discrimination and detection of pulse changes in color. Experiments on the variation in color discrimination over color space under condiitions of constant adaptation will be continued and extended. These experiments should lead to new standards with which to describe color discrimination in everyday life. Theoretical analysis of the factors that control the detectability and appearance of brief, small monochromatic lights is proposed. The results of this analysis should help in generating estimates of the distribution of the different classes of cone receptors. Experiments are proposed on the role of color in the detection of motion. These experiments should help in determining the stage at which signals from the separate ,second stage mechanisms interact. Experiments are planned on the influence of color on the ability to judge the crientation of lines. These experiments should provide information on the ability of chromatic mechanisms to process spatial information. Recording of the magnetic fields generated in response to chromatic and luminance Ipulses will be made. The goal of these experiments is to see whether this method will provide evidence to support the theory that information about the chromatic and achromatic aspects of stimuli are transmitted through separate neural systems. Continued collaboration in studies of the properties of single neurons in the monkey i,visual system is planned. Methods which have proved fruitful in the characterization of !units in the lateral geniculate will be applied to cortical systems in Vl, V2, and V4.